Halstead and Essex marathon if you don't mind a feww hills. Not sure about bling, though.
I use an OMM 'Last Drop' rucksack which is light and comfortable. It's fairly small at 10 litres, and currently on sale at Sweatshop. I'd second the advice to leave what you can at work, and minimise what you carry.
Well done on securing a place!
You could take a look at the ASICS website which can produce a tailored training plan.
Good idea to stick with strength training, and don't forget core strength, stretching and flexibility too.
Have you looked for gloves online at sportsshoes.com?
The Stour Valley Path "SVP100" is a worth considering in its 3rd year next August. It is 100km of scenic off-road route from Newmarket to Brantham.
It was well-organised, friendly, clearly marked route with excellent checkpoints/food/water stations.
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